Method and apparatus for processing vitreous melt

ABSTRACT

A melt of vitreous material is heated uniformly by means of a heat tube or heat pipe, wherein circulation of a heat-exchange medium is effected independently of gravitational forces and exclusively as a function of a temperature differential existing within the heat tube. Various apparatus for accommodating and extruding melt of vitreous material are disclosed, and utilize the heat tube in different forms for controlling the temperature of the melt in desired manner.

0 United States Patent [151 3,640,517 Sendt 1 Feb. 8, 1972 [54] METHOD AND APPARATUS FOR [56] References Cited PROCESSING VITREOUS MELT UNITED STATES PATENTS [72] Inventor: Alfred Sendt, Guetersloh, Germany 3 495 966 2/l970 West 65/346 X [73] Assignee: Hermann Heye, Obernkirchen, Germany 3,265,485 8/1966 Carney et al ..65/346 X [22] Filed: Apr. 2, 1970 2,840,351 6/1958 Holm ..l65/l05 X PP NOJ 25,103 Primary Examiner10hn J. Camby Attorney-Michael S. Striker [30] Foreign Application Priority Date Apr. 3, 1969 Germany ..P 19 17 450.6 [J7] ABSHMCT July 22, 1969 Germany ..P 19 37 124.5 A melt of vitreous material is heated uniformly by means of a heat tube or heat pipe, wherein circulation of a heat-exchange U-S. medium is effected independently of gravitational forcgs and I Int C F27) exclusively as a function of a temperature differential existing I58} Field of Search ..263/11, 14;65/34 6, 347,337; the .heat tube Y appaiams l [65/105 and extruding melt of v1treous material are disclosed, and utilize the heat tube in different forms for controlling the temperature of the melt in desired manner.

53 Claims, 24 Drawing Figures PATENTED FEB 8 I972 SHEET 2 0F 7 w w M 7 1 W 0 M. \I V? m v/h// V FIG 7 /N VE N TOR Alfred SENDT Jhollb his ATTORNE Y PATENTEDFEB 8 i972 SHEET 3 0F '7 FIG.8

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INVENTOR: Alfred SENDT B di /ll! l/lrf hI S ATTURNE Y PAIENTEDFEB 8 I972 33, M051 '7 saw u or 7 i INVENTOR Alfred SENDT his ATTORNEY PATENTEDFEB 8 I972 3940951 7 sum 5 or 7 zso Z52 INVENTORI Alfred SENDT his A TTORNE Y PMENTEU EB 8 I972 3,640. 51?

sum 5 or 7 FIG. 17 5 21 FIG. 18 ////4/ FIG. 79 223 INVENTOR 1 Alfred SENDT his A TTORNE Y FIG. 22

323 323 T T T325 m- T m 315 m INVENTOR: Alfred SENDT i'umm,

his ATTORNEY METHOD AND APPARATUS FOR PROCESSING VITREOUS MELT BACKGROUND OF THE INVENTION The present invention relates generally to the treatment of a melt of vitreous material, such as glass, with respect to its temperature. More particularly the invention relates to the controlling of the temperature of a vitreous melt under various circumstances.

It is well known that the quality of articles made from the vitreous material, particularly articles of glass and especially those which are hollow, such as bottles, hollow glass guilding blocks, television tubes and the like, is significantly influenced by the temperature conditions which prevail in the melt in the various stages of the glass-making process, that is from the time the melt is formed until the time glass is made by converting the melt into a desired article. Because of this industry has attempted again and again to influence these temperature conditions in a sense obtaining optimum circumstances and to make them reproducible at will, depending upon the prevailing technological and methodological circumstances. However, none of the many prior art attempts in this direction have been as successful as was hoped and desired.

Thus, the melting effectiveness in crucibles is a function of the heat exchange between the melting flame and the glass in the crucible. Among the attempts which have been made to increase this heat exchange effectiveness is the insertion of metallic inserts, for instance of molybdenum sheet metal, in the melt accommodated in the crucible in such a manner that the upper portion of the inserts is so positioned that they will absorb heat, substantially by radiation, and convey such heat to lower portions located in lower layers of the melt. Such a proposal has for instance been made in Untersuchungen zur Anwendung warmeleitender metallischer Einbauten in Wannenoeffen zur Homogenisation der Schmelze by S. Speth in Symposium sur le contact du verre chaud avec le metal," pp. 396-409, Scheveningen I964.

However, it has been found that the heat conducting ability of these inserts, that is the ability to convey heat to the surrounding melt, decreases continuously with increasing depth of immersion in the melt. The reason for this is that quite rapidly the inserts reach the temperature of the surrounding glass melt and thus become completely inefficient. This has been found especially when an attempt was made to bend these inserts so that their lower portions would extend in parallelism with the bottom of the crucible.

Another attempt to supply substantial heat energy to the melt contained in the crucible utilizes an electric resistance heating system provided with electrodes which extend into the glass melt. This is not the main source of heat, but an auxiliary heating system in addition to the main source. The problem is that with this proposal high localized temperatures develop, and in certain circumstances this is not acceptable with respect to the stresses on the crucible itself. Furthermore, it is clear that the material required for the electrodes which are immersed in the melt, and the expense of supplying electrical energy for the necessary heat, make this approach so costly that it is economically unsound. In addition it has been found that even with this proposal it is usually still necessary to provide artificial convection in the melt by blowing air into the bottom of the crucible.

SUMMARY OF THE INVENTION For the above reasons, and others which will be discussed subsequently, it is a general object of the present invention to provide for improved temperature control of vitreous melt from the time the melt is accommodated in the melting crucible to the time at which the melt is converted into a glass article.

More particularly it is an object of the present invention to provide a novel method of affording such improved temperature control.

An additional object of the invention is to provide apparatus affording such temperature control.

Another object of the invention is to provide for such temperature control of the melt that the glass articles manufactured from the melt have a quality which is at least equal to that obtained with glass melt whose temperature is controlled in accordance with the prior art, and which is preferably superior.

Still another object of the invention is to provide as homogenous as possible temperature conditions in a body of melt, and to avoid devitrification of portions of the melt due to the presence of local cool areas in the body of melt. At the same time, the formation of local "hot spots as a result of excessive flame heating during temperature increase of the body of the melt is also to be avoided.

A concomitant object of the invention is to provide for maximum possible thermal homogenization of the vitreous melt in feed or supply channels which convey the melt away from the crucible to other processing stations.

Another object is to provide not only for thermal homogenization of the melt in such supply channels both in longitudinal and transverse direction of the same, but also for a rapid but gentle variation in the melt temperature in case of a change in the melt throughput quantity for a feed channel.

An additional object of the invention is to provide for a reduction in the necessary heat or supply channel length.

Still a further object of the invention is to provide apparatus which guarantees that any individual quantity of melt is of homogenous temperature, that successive quantities of melt are of identical temperature.

Yet an additional object of the invention is to provide for homogenization of thermal conditions in a melt in a melting crucible.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of the invention resides in a method of controlling the temperature of a melt of vitreous material, according to which the temperature of a vitreous melt is controlled by heat exchange between the melt and heat exchange means in form of a heat tube constituting a closed circulatory system which accommodates a liquid vaporizable heat exchange substance and a capillary structure for conveying or at least facilitating transportation of condensed heat exchange substance within the system to a region in which the substance is subject to renewed vaporization.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a section through a melt-containing crucible taken on the line II of FIG. 2;

FIG. 2 is a section taken on the line II-II of FIG. 1;

FIG. 3 is a section analogous to that of FIG. 1 through a further crucible;

FIG. 4 is a diagrammatic perspective view of a feed conduit according to the invention;

FIG. 5 is a cross section through a feed conduit similar to FIG. 4 but according to a further embodiment of the invention;

FIG. 6 is a sectional view of a connection between several heat tubes in a system of such heat tubes;

FIG. 7 is a fragmentary longitudinal section through a heat tube provided with several types of protective means against corrosion damage;

FIG. 8 is a section on line VllI-VIII of FIG. 9 through a further feed conduit according to the invention;

FIG. 9 is a section taken on line IX-IX of FIG. 8;

FIG. 10 is a cross section through a further feed conduit according to another embodiment of the invention,

FIG. I! is a fragmentary section through a heat tube partially projecting from the body of melt with which it is to effect heat exchange;

FIG. 12 is a section on line XII-XII of FIG. 13, showing an extrusion head according to the present invention,

FIG. 13 is a section on line XIII-XIII of FIG. 12;

FIG. 14 is a section on line XIVXIV of FIG. 13;

FIG. 15 is a section, on an enlarged scale, through the feed tube concentric with the outlet opening of the device shown in FIG. 12;

FIG. 16 is a view analogous to FIG. 12 but showing a further embodiment;

FIG. 17 is a view similar to FIG. 16 showing still another embodiment of the invention;

FIG. 18 is a section taken on line XVIIIXVIII of FIG. 17',

FIG. 19 is a section taken on the line XIXXIX of FIG. 18;

FIG. 20 is a cross section through an extrusion ring according to the present invention;

FIG. 21 is a view similar to FIG. 20 but illustrating a different extrusion ring;

FIG. 22 is a diagrammatic longitudinal section through a melting crucible embodying the invention;

FIG. 23 is a section taken on line XXIIIXXIII of FIG. 22; and

FIG. 24 is a section on an enlarged scale taken on line XXIV-XXIV of FIG. 22.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before entering into a detailed discussion of the individual Figures and embodiments, explanatory comments are necessary. Firstly, it is necessary to point out that the concept of a heat tube per se is already known. Such a heat tube is described in US. Pat. No. 2,350,348 and in the corresponding German Pat. No. 833,500. It is also described in the article Das Waerrnerohr (Heat Pipe)" in the publication Chemiclngenieur-Technik, published by Chemie G.m.b.H I967, vol. I, pp. 2l-26. However, in these prior publications the heat tube has been used in cryogenic applications only and in space flight applications, namely in energy supply units for spacecraft. The new heat pipe, as it will hereafter be designated for the sake of convenience, circulates a liquid vaporizable heat-exchange medium in a tube constituting a closed circulatory system, independently of gravitational influence and solely as a function of the presence of a tempera ture differential. It is based on the capillary principle and the principle of surface tensions of liquids. A pipe is used containing a capillary structure which is saturated with the heatexchange medium, with the latter being expelled from the capillary structure as a result of heating to the point where the heat-exchange medium becomes vaporized. The vapor flows in the direction of the temperature decrease and then condenses, yielding heat of condensation. The capillary structure serves to return the condensed heat exchange medium or substance to that area of the pipe where vaporization takes place.

Utilizing a heat-exchange pipe operating on this principle, it is possible in accordance with the present invention to effect heating or cooling of a glass melt within narrow limits and in a self-regulating manner. It will be appreciated that both cooling and heating of the melt can be effected in this manner, for instance heating of the melt in the so-called cold zones in which devitrification can occur with the result that crystals forming in such zones are carried along by the melt and appear in the finished glass product as visible flaws. It is further of particular importance that the use of the heat pipe in the application according to the present invention affords a selfregulating thermal homogenization of the glass melt within narrow limits.

In an apparatus according to the present invention one or more heat pipes may be incorporated in a vessel adapted to contain the vitreous melt, and such pipes may extend from a higher or upper to a lower strata of melt in the vessel. The superior heat-exchange capability afforded by the heat pipe assures that, if for instance the heat pipe is heated by the heat of the melting flame acting upon the upper or higher strata of the melt, such heat is rapidly and substantially without temperature losses transmitted to all such portions of the heat pipe as are initially cooler than the portion which has just been subjected to the heating. The result of such heat conducting efficiency is that the pipe will have everywhere substantially the same temperature at identical wall thickness, independently of the geometric configuration of the pipe. The result is that the heat energy level prevailing in the upper stratum or strata of the meltand which acts upon the corresponding portion of the heat pipe-is thoroughly, rapidly but gently transmitted to the lower strata of the melt by the pipe. The pipes may be arranged vertically or substantially vertically. Furthermore, two or more heat pipes may be axially aligned and may but need not be exteriorly connected with one another. In this manner it is possible to use heat pipes of identical length-thereby simplifying manufacturing and stocking problems-for bridging distances of different lengths greater than the unit length of the individual pipes. Further, two vertically or substantially vertically arranged pipes which are axially consecutive may overlap one another, that is the lower end portion of the upper pipe may overlap the upper portion of the lower pipe to some extent in the zone in which they overlap, heat energy can be transmitted from one to the other of the pipes.

One or more of the pipes arranged in this manner in a vessel accommodating a vitreous melt may have their lower portions extending at an angle to their upper portions in such a manner that the lower portions extend in parallelism or substantial parallelism with the bottom wall of the vessel. These lower portions may be located in the proximity of the bottom wall, or in contact with the same. In this manner a particularly intensive transport of thermal energy is guaranteed to those portions or areas of the vessel which are least likely to receive thermal energy from the flame acting upon the upper stratum of the melt.

Furthermore, one or more of the heat pipes may have their upper portions so bent that they extend in parallelism with and proximal to the upper level of the melt in the vessel. This makes it possible to have the heat pipe or pipes absorb heat energy for transmission predominantly at such areas of this,

upper level which are subject to especially intense heating by the flame.

The invention makes it possible in particular to provide a crucible which is especially suitable for the production of special vitreous melts, for instance melts for optical glass, in which the melting capacity is increased and the reduction of quality of the melt due to local overheating or cold spots with subsequent devitrification is prevented. Further, the supply vessel which receives melt from the crucible and passes it on to further processing stations, in effect constitutes an intermediate storage location for the melt. Its purpose is to provide a thermal calming" and a thermal homogenization as well as a reduction in the temperature of the melt. Known storage or supply vessels of this type are provided with top heating by means of gas or oil burners. However, it is well known that such heating alone is not sufficient to produce and maintain in the melt accommodated in the storage vessel, as it will hereafter be called for the sake of convenience, the desired uniform temperature conditions. The invention provides for a sufficient prehomogenization of the temperature of the melt in the storage vessel, and avoids cold spots" where devitrification can occur as well as locally overheated spots.

The invention therefore proposes a storage vessel containing one or several three-dimensional heat pipe systems. These can be so conflgurated that in effect the temperature in every area within the storage vessel can be regulated as desired. Thus, heat is transported by these heat pipe systems from overheated areas to those which are underheated, to thereby produce a uniform temperature in the melt. The arrangement of the system or systems of heat pipes can be such that it extends throughout or substantially throughout the entire body of melt which is accommodated in the storage vessel. Of course, only a single heat pipe arranged and conflgurated in desired manner can be utilized, or several individual heat pipes can be used which for heat exchange purposes locally approach one another or are locally connected with one another. The connection can be such that only the outer surfaces of the tubes or pipes, or their inner surfaces and capillary structures are connected with one another. In the latter case it will be appreciated, of course, that the temperature of the thus-connected pipes will be substantially uniform throughout.

it is particularly simple and inexpensive to construct an arrangement if each such above-mentioned system is composed of a grid of straight heat pipes. If the system is completely immersed within the body of melt and no heat pipes extend through the walls of the storage vessel, then it is at most possible to influence the temperature of the system from the exterior by indirect means, for instance through the direction and radiation of the flame of a burner acting upon the melt. However, it is also possible to directly effect temperature control of the system through exterior measures, in which case a control arrangement may be provided which is preferably located exteriorly of the body of melt and which may be controllable or regulatable, such as a blower or a water jacket, in which case at least one heat pipe of the system or systems may for instance extend upwardly through the upper level of the body of melt and be coupled with the tempering device. Where the pipe crosses through the upper level of melt it must be provided with anticorrosion means, for instance by encircling it with a platinum ring. This prevents corrosion of the material of the pipe which otherwise would take place. it is of course also possible to effect coupling of a system of the aforementioned type with a temperature control device in that at least one heat pipe of the system passes out of the body of melt below the upper level thereof, through a wall-that is either a sidewall or the bottom wallof the storage vessel, in which case it must of course be sealed where it penetrates the wall.

The problems which the present invention seeks to overcome are particularly bothersome in the feed or supply conduits. The machines receiving the melt for further processing require for maximum performance that each individual quantity of melt received be thermally homogenous, i.e., be of uniform temperature, and that the temperature of successive quantities of melt be as near identical as possible. Temperature variations between individual quantities of melt may for instance influence the weight of the quantity of melt, its form with respect to length, cross section and straightness of its axis, and they may influence the operating circumstances of the machine, for instance by adversely influencing the operation of the machine which is set in consideration of a particular melt temperature.

it is further necessary that the aforementioned so-called cold spots be avoided everywhere in the supply conduit, because they could result in devitrifrcation with the earlier described disadvantages. Furthermore, controlled decrease of the melt temperature is to take place in the supply conduit, and this depends upon a number of factors, for instance upon the type of glass involved. Thus, if the glass is so-called brown glass, a uniform temperature decrease of the melt between the supply vessel and the outlet nozzle supplied by the supply conduit is particularly important because overheating or excessive temperature decrease, both of which frequently occur in constructions according to the prior art, can cause substantial damage, for instance in terms of insufficient color contrast and the formation of bubbles. On the other hand, ground glass melt has a relatively poor thermal conductivity so that heat does not readily permeate the melt, making it difficult to provide sufficient temperature increases-where cold spots are to be eliminated--over a relatively short flow path afforded by the supply conduit.

The prior art provides very elaborate attempts at affording uniformity of heat of melt in the supply conduit, both lengthwise and transversely of the latter. It is known, for instance, to use mechanical stirring devices in the supply conduit, and the construction disclosed in U.S. Pat. No. 3,224,857 is representative of this approach. However, the efficiency of these devices is limited, even if several of them are provided.

A further problem encountered in this context are the temperature changes of the melt which are necessary when for instance the weight of the individual quantity of melt supplied to the machine is to be changed, because of the limited heat conductivity throughout the melt and the occasional special temperature sensitivity of certain types of melt. These are particular problems which have not yet found a solution in the prior art, despite complicatedv and expensive regulating devices and despite substantial increases in the length of the supply conduits which, it was hoped, would facilitate the necessary control.

These problems are overcome according to the present invention by providing inthe supply conduit one or several heat pipe systems which may be so contigurated, dimensioned and positioned that excellent uniformity of the temperature of the melt in the supply conduit is achieved. Furthermore, it is now possible to provide for a much more rapid changeover of the production from smaller melt quantities to larger melt quantities and weights, and vice versa. Where such changeover in known constructions frequently requires several hours, the present invention permits it within a much shorter span of time. Overheating of the melt is avoided and the length of the supply conduit may be decreased. Mechanical stirring devices are completely or largely obviated and a more uniform heating and cooling-depending on local temperature conditions-of the melt is afforded. Each of such heat pipe systems in the melt supply conduit may be constructed analogously to the details mentioned above with respect to their use in the supply vessel. Several heat pipes may extend in parallelism with the direction of flow of melt through the conduit proximal to the bottom wall of the latter, and they may each have at least one end portion which extends upwardly. Those portions which extend in parallelism with the flow of the melt provide for a continuous temperature of the melt flowing through the supply conduit, while the upwardly extending end portions provide for a transverse heat exchange between different strata of the melt flowing through the conduit, that isheat exchange transversely to the direction of movement of the melt. This can be further facilitated by providing additional heat pipes of substantially U-shaped outline which extend transversely to the pipes extending lengthwise of the supply conduit and whose legs extend upwardly. Of course, here also the individual heat pipes may be connected with one another, or may locally approach one another for heat exchange purposes.

lf the level of melt passing through a supply conduit is relatively low, the heat pipe system may use several straight longitudinally extending heat pipes which extend in parallelism with the direction of flow of the melt, substantially in a common plane, and which may or may not be connected transversely with one another by one or more additional heat pipes. One end of the supply conduit in known manner is a so-called supply head having an outlet opening and a nozzle ring connected therewith. To assure proper and uniform formation of drops or gobs of melt or parisons or individual quantities of melt at the nozzle ring, it is necessary that within the region of the headthe melt be either maintained at uniform temperature, or be given uniform temperature if it does not already have it. For this reason the prior art teaches the use of a separate top or upper heating arrangement utilizing gas or oil burners in the region of the supply head, as well as rotation of the plunger and a turnable tube which is coaxial with the same. However, experience has shown that these known attempts are not adequate for producing and maintaining the desired optimum temperature conditions in the melt.

The present invention overcomes these problems by locating in the region in question, that is in the melt in the supply head, one or more heat; pipe systems. The thus-constructed supply head may of course be supplied with melt by a supply conduit which itself is constructed according to the present invention. In this manner regulation of the temperature of the melt can be carried out over a relatively long distance at lower specific stresses upon the melt.

The wall of the outlet opening in the supply head may itself be configurated as a heat pipe in accordance with the invention. in certain applications this alone without the provision of additional heat pipes will be. sufficient for obtaining the necessary thermal uniformity of the melt. In this construction the wall may have a cylindrical inner surface and an outer surface which is coaxial with and outwardly spaced from the inner surface and fluid tightly connected therewith, with the juxtaposed sides of the same being provided with capillary structure. The wall having the outer surface may either be cylindrical itself, or if it is desired to increase its wall surface area, it may be outwardly bowed. The outer side of the wall having the outermost surface may also be provided with a temperature regulating device, or connected therewith for heat exchange purposes in the sense described earlier.

According to a further embodiment of the invention one or several rings or sections or rings composed of heat pipe may be provided coaxially with the outlet opening of the supply head. This provides a concentric temperature regulation of the glass melt, adapted to the flow conditions of the glass melt. For providing a particular temperature influencing of the glass melt one or several of the rings or sections of rings may be providedwith projections or extensions of heat pipe which extend in the direction of the advancing melt, that is oppositely to the direction of advancement of the same. It is also possible to arrange coaxially with the outlet opening of the supply head a helically convoluted heat pipe which also circularly influences the flowing melt.

On the other hand, one or several plates may be provided each of which is provided with an embedded net of heatexchange pipes. These plates prevent direct contact between the melt and heat-exchange pipes and at the same time serve as a heat-storing and thermally damping medium interposed between the melt and the heat pipes. The outline of each plate may for instance correspond to the free cross section of the supply head. Each plate may also extend substantially in parallelism with the direction of flow of the melt. It is particularly advantageous if such a plate is arranged on or in the bottom wall of the supply head. One or more additional such plates may be arranged above this first plate and supported either by supports of heat pipe or simply by supports of material which is not subject to destruction by contact with the melt. The plates may consist of metal which is either noncoloring or provided with a noncoloring layer, for instance of a ceramic material. According to an embodiment of the invention at least one such plate extends into the supply conduit, and it will be appreciated that if desired or necessary the entire supply conduit may be provided with one or several of such plates itself.

The nozzle ring from which drops of melt issue after passing through the outlet opening of the supply head, may also be provided interiorly with a heat pipe structure. Such an arrangement in particular avoids the thermal difficulties which exist in known multiple-drop nozzle rings at the space between the individual drop outlets. These portions of the ring which define such spaces heretofore are cooled only with air and in insufficient manner, so that quite frequently undesired form changes of the issuing drops occur as a result of the differential temperature conditions at the circumference of the issuing drops. It is also possible, however, in accordance with the present invention to surround each drop outlet of the ring externally with a heat pipe structure. In this case the latter is subjected to lower temperatures, but as in the preceding embodiments a temperature is obtained and enforced for the issuing drop or quantity of melt or parison, which is even over the entire circumference of the same.

In a heat pipe for use in accordance with the applications outlined above, at least those surfaces of the pipe which come in contact with the melt consist of material which is inert and resistant to the melt, for instance ceramic, certain metals or a cover of ceramic or such metals. n the one hand this avoids deleterious influences of the heat pipe on the melt, for instance color changes of the melt through the intrusion of oxides and on the other hand it avoids damage to the heat pipe itself. According to one embodiment at least those surface portions of the heat pipe which are located outside the melt are provided with a coating of corrosion resistant material, for instance ceramic, which surrounds the heat pipe with spacing, with the space being fillable with melt. in this manner a corrosion of the heat pipe outside of the melt is avoided and the melt accommodated in the space serves at the same time as a heat-exchange contact means if, in accordance with the present invention, the outer side of the cover is coupled in the aforementioned manner with a temperature regulating device.

A particular problem posed by glass melts are such melts, and particularly specialty glass melts, in melting crucibles. The latter of course are known and are predominantly used for melting of special glasses which are usually expected to be of exceptionally high quality. The final quality largely depends upon the temperature conditions within the melt contained in the melting crucible and many attempts have therefore been made to provide for optimum temperature conditions under the circumstances. However, they have not been as successful as desirable. Of course, the present invention can overcome or at least alleviate these problems by utilizing in such melting crucibles the same arrangement of heat pipes as has been set forth with respect to other types of vessels. In particular, the sidewalls and/or the bottom wall of such a melting crucible may be of double-walled configuration and the space between the inner and outer wall may be constructed as a heat pipe. In this manner control of the temperature of the outer surface or outer wall of the melting crucible and thereby of the melt itself can be carried out at any desired points of the outer surface of the crucible in any desired manner, for instance by gas heating or by means of electrical resistance heating. Theoretically control of the temperature of a very small area of the outer wall of the crucible would be sufficient to obtain an excellent thermal homogenization of the melt accommodated in the melting crucible.

However, the sidewall and/or the bottom wall of such a melting crucible may also be provided with several recesses into which inserts can be placed which are configurated as heat pipes. Such inserts may be solder connected or otherwise connected with the crucible to further the heat exchange between insert and crucible. In this construction it is advantages that such inserts can be locally introduced at points of the crucible which require special tempering treatment. Another advantage is the fact that the inserts can be reused even if the crucible itself has become damaged beyond repair and must be replaced. Furthermore, a single set of such inserts may serve to effect control of the temperature of the melt in several melting crucibles either sequentially or simultaneously, assuming in the latter case that not all inserts are needed at any one time for tempering a single crucible.

If it is desired to control or regulate the heat-exchange effect of several of the inserts in unison, then these can be connected with one another by heat pipe sections. It is also possible to have one or several heat pipes extend into the melt, the purpose being to guarantee the desired thermal conditioning of the melt even if the influencing of the melt temperature for instance in the case of very large crucibles-from the inner wall of the crucible alone is not possible. This assumes, of course, that the crucible is of the type utilizing a double wall which is itself constructed as a heat pipe. In such latter type of construction the additional heat pipes extending from exteriorly into the body of melt in the crucible may be connected with temperature control devices located exteriorly of the melt.

Discussing now the drawing in detail, and firstly the embodiments in FIGS. 1 and 2, it will be seen that in these Figures l have illustrated a melting crucible 30 which is filled with a body of vitreous melt 32 to a level 31. Upwardly of the level 31 at opposite sides of the crucible 30, there are provided supply conduits 33 and 34 for combustible fuel, such as gas, oil or the like, and air supply conduits 37 and 38 which communicate with the laterally located regenerating chambers 39 and 40.-

Constructions as thus far discussed are known in the art.

In accordance with the present invention, however, I provide heat-exchange means in form of heat pipes 43-46 which are arranged vertically or substantially vertically in the melt 32, being maintained in their desired position by nonillustrated suitable means, such as ceramic stands, ceramic holders or the like. The cross-sectional configuration of these heat pipes 43-46 may be selected, for instance, in accordance with the considerations discussed subsequently in connection with the embodiments of FIGS. 7 and 14.

As illustrated, at least one of the heat pipes, namely the one identified with reference numeral 43, has an upper portion 47 which extends below the level 31 in at least substantial parallelism therewith. The heat pipe 43 is further provided with a lower portion 49 which extends in parallelism with the bottom wall 50 of the crucible 30, being spaced from but proximal to the bottom wall 50. However, it is emphasized that the portion 49 can also be in contact with the bottom wall 50. It will be appreciated, of course, it is equally possible for portions analogous to those identified with reference numerals 47 and 49 to be provided on one of the other heat pipes instead of the heat pipe 43, or to provide more than one of the heat pipes with such portions.

The drawing shows that the heat pipe 45 consists of two axially arrayed discrete heat pipes 53 and 54 which are in axial alignment and which at their point of connection 55 are belled for facilitating heat exchange between the two conduits 53 and 54.

A further possibility is illustrated with respect to the pipe 46 which is composed of two discrete conduits 57 and 58 each of which is of course sealed by itself and which have adjacent end portions so arranged that in vertical direction-with respect to the crucible 30-they overlap to some extent as illustrated, to thereby provide for heat exchange between the overlapping portions. These, incidentally, could also be connected exteriorly with one another, for instance by being in contact or by being connected with thermally conductive material.

It is specifically emphasized that all of these various constructional possibilities for the heat-exchange pipes which have been illustrated in FIG. 1, can be employed in a single apparatus. Of course, it is also possible to employ only a single one, or two, of these different possibilities in one apparatus.

Furthermore, it will be appreciated that fewer or more heatexchange pipes then illustrated can be employed, depending entirely on the circumstances of a given case, that is how the temperature of the melt in the crucible 30 is to be regulated, that is locally heated and/or cooled in order to obtain throughout a uniform temperature. Furthermore, FIG. 2 shows that additional heat pipes 60 and 61 can be arranged so as to be immersed in the melt, and these correspond to the heat pipe 43.

In FIG. 3 a melting crucible is again identified with reference numeral 30 and provided with heat pipes 63-65 the lower end portions of which are angled with respect to the remainder of the respective pipe and extend in parallelism with the bottom wall 50. The remainder of each of the pipes is arranged in a vertical plane. It is advantageous to provide several sets of such pipes 63-65 which are located in different planes in the respective vessel, that is here the melting crucible 30.

FIG. 4 shows a supply conduit which supplies vitreous melt from the crucible 30 via a supply vessel to a processing station. The supply conduit is identified with reference numeral 70 and essentially it comprises a bottom wall 71, sidewails 72 and 73 and a cover 74 as shown in FIG. 5. It is emphasized that in essence the basic construction of the conduit 70 corresponds to that of a supply vessel, except for the different configuration and for the fact that in the supply vessel the melt is accommodated for withdrawal into the conduit 70, whereas in the conduit 70 the melt moves along the latter. It will be remembered that the supply vessel is interposed between the melting crucible 30 and the conduit 70, with the latter receiving the melt from the supply vessel rather than directly from the melting crucible. It will also be recalled that it has been stated before that a supply vessel is to be constructed, in aceordanee with the present invention, in such a manner as to permit regulating of the temperature of the melt accommodated therein by utilizing the already described heat pipes. However, because of the close analogy in the constructions of such supply vessels and the conduit 70, a separate supply vessel has not been illustrated in the drawing, and it is pointed out that the construction of the conduitexcept for its overall configurationis analogous to that of a supply vessel to obviate the need for a separate illustration.

Keeping this in mind it is pointed out that the following comments with reference to the construction of a supply conduit 70 provided in accordance with the present invention with the heat pipes to be discussed, applies analogously to the construction of such a supply vessel.

It will be seen from FIGS. 4 and 5 that the supply conduit 70 is provided with two sets or systems of heat pipes, with each set being identified with reference numeral 75 and 76, respectively. The direction of flow of the melt through the conduit 70 is identified with the arrow 77, and the two sets 75 and 76 are arranged spaced from one another in the direction '77.

Each of the sets 75 and 76 is composed of a three-dimensional grid of straight heat pipes 80-82. Of these, the heat pipes 80 and 81 are so connected as to define with one another a planar vertically oriented grid. The two grids of the sets 75 and 76 are then connected by the longitudinally extending heat pipes 82. It is emphasized that the various heat pipes 80-82 may be placed into engagement with one another at their respective crossing points, and may be connected only at such crossing points, or that they may be inserted into a connecting block 85 provided at the crossing points and serving to maintain the heat pipes in their respective positions as well as to facilitate heat exchange between them.

A thermal element 87 is inserted into the conduit 70 at a suitable point, herein the region of the second set 76, and serves to control a nonillustrated temperature-regulating device. FIG. 5 further shows the provision of an additional three-dimensional grid composed of heat pipes 91-93, which grid differs from those identified with reference numerals 75 and 76 and is located below the upper level 89 of the melt 90 with the lower crosswise-extending pipes 92 being directly supported on the bottom wall 71 of the feed or supply conduit 70 FIG. 6 illustrates a connecting element 95 corresponding to the previously discussed block 85. The heat pipes 80-82 are each sealtightly connected with a housing 97 the interior of which is provided with capillary structure 98 which is in contact with the capillary structure 99-101 accommodated in the heat pipes 80-82, via openings provided in the housing 97. In this connection it is pointed out that for details of the capillary structure and materials suitable therefor, as well as of the heat-exchange liquid which circulates in the respective heat pipes, reference may be had to the aforementioned patents and publications where such information is disclosed in detail. The information is therefore available to those skilled in the art and is not thought to require specific reiteration herein.

Coming to the embodiment in FIG. 7 it will be seen that this is a cross-sectional view through a heat pipe 137 provided on its inner side with capillary structure 138. If there is any danger that the exterior of the heat pipe 137 might be subject to corrosion, then the exterior can either be coated with the corrosion-resistant or corrosion-free layer 139 of a suitable material, such as ceramic, or the exterior of the heat pipe 137 may be surrounded with spacing by a jacket 140 of such corrosion-resistant or corrosion-free material. It is particularly advantageous to fill the space between the he at pipe 137 and the jacket 140 with vitreous melt and to prevent the circulation thereof, if at all possible, because this guarantees that no substantial quantities of oxygen can be carried to the outer side of the heat pipe 137 so that the danger of corrosion is eliminated.

Coming to the embodiment of FIG. 8 it will be seen that this illustrates a supply conduit which terminates in a supply head 107 having an outlet opening 108 and a tumable tube 109 arranged thereabove. The conduit 105 and the head 107 are provided with covering means 110 and containing vitreous melt 111 to an upper level 112, with the melt issuing from the head 107 in the direction of the arrow 113. It will be appreciated that in such supply heads there is usually provided a plunger mechanism for expressing quantities of the melt from the outlet nozzles; because this does not form a part of the present invention and for the sake of clarity of illustration, such mechanism has been omitted here.

As FIG. 8 shows clearly, a plurality of longitudinally extending heat pipes 117-119 is arranged proximal to the bottom wall 116 of the supply conduit 105, extending in the flow direction 115 of the melt 111. At one end these heat pipes 117-119 are provided with an upwardly angled section, such as the one identified with reference numeral 121, which extends, upwardly through the cover 110 and is surrounded with spacing by a jacket 123 of corrosion-resistant material, such as ceramic, in the manner discussed above with reference to FIG. 7. As mentioned before, the space defined between the respective section and the jacket 123 may be filled with vitreous melt, not only for corrosion protective purposes but also for facilitating heat-exchange characteristics. If the wall of the heat pipes, or at least of the sections extending upwardly above the level 112 of the melt 111, consists of noncorroding material or is coated with such, the jacket 123 may be omitted.

The temperature of a portion of the outer surface of the jacket 123 is controlled by a temperature control device 125 through which a heat-exchange medium such as air, flows in the direction of the arrows 126.

As shown in FIGS. 8 and 9, there are further provided in this embodiment transversely extending heat pipe 130-134 immersed in the melt 111 and extending to differential depths with respect to the upper level 112. They are substantially U- shaped in outline and the heat-exchange pipe 130 is completely immersed below the level 112 and thus not subject to corrosion-causing influences above this level. It is supported on the bottom wall 116 of the conduit 105 by means of ceramic holders 145 and 146.

The heat pipes 131-134 are secured to the cover 110 and may, if desired or necessary, be further supported on the bottom wall 116 by means of ceramic holders or stands. Those portions of the heat pipes 131-134 which extend out of the melt 111 may be connected with temperature control devices 1 corresponding with or analogous to the device 125 previously discussed. It is clear from FIG. 9 in particular that substantially the entire cross section of the supply conduit 105 is subject to the influence of heat pipes in the embodiment of FIGS. 8 and 9.

As FIG. shows, if the melt 147 flowing in a supply conduit 148 is of relatively small depth, it is sufficient to use several straight longitudinally extending heat pipes 149-152 for influencing and controlling temperature conditions in the melt 147. In this embodiment the pipes are located in a plane of the melt which extends in parallelism with the flow direction of the latter; if desired or necessary a cross-connection 154 may be provided for the pipes 149-152, also consisting of heat pipe.

In the embodiment of FIG. 11 a temperature control device 53 is shown for that portion of a heat pipe 156 which projects upwardly out of the upper level 155 of a vitreous melt. The heat pipe 156 is for instance provided as a molybdenum pipe 157 provided at the upper end with an enlargement 157 and carrying on its inner surface capillary structure 159. In the region in which the heat pipe 158 passes through the upper level of the melt, the level being identified with reference numeral 155, it is surrounded by a corrosion-protection platinum ring 161 which is to prevent erosion of the material of the heat pipe 158 in the region of the level. Ifthe material of the pipe 158 or the enlargement 157 is in danger of corrosion, it may be provided at least in the region coming in contact with the medium 163 with a corrosion-resistant coating 164, for instance of gold.

A further embodiment is shown in FIG. 12. Here, a supply conduit 167 is illustrated which terminates in a supply head 168. Arranged below the level 170 of the melt 171 in the conduit 167 there are provided heat pipes 173-175; in the supply head 168 there is provided a stack of heat pipes 177-180. The latter heat pipes are substantially coaxial with an outlet opening 183 of the supply head 167, and with a turnable tube 185 located above the outlet opening and passing through a cover 184; the heat pipes 177-180 are supported on ceramic supports 187-189, except for the lowermost heat pipe which is directly supported on the bottom wall 191 of the supply head 168. The configuration of the heat pipes 177-180 is substantially ring shaped in outline and open-although this is not necessaryin the direction of the melt arriving from the supply conduit 167. This opening is identified with reference numeral 191 in FIG. 13 with reference to the heat pipe 168. In the case of the heat pipes 177-179 the corresponding opening has the outline of a semicircle. In the heat pipes 177-179 there is provided at each free end connected to the semicircle of the respective heat pipes, such as identified with reference numeral 193 and 194, which extend in the direction of the supply conduit 167. A circularly configurated heat pipe'197 is inserted into the outlet opening 183 of the supply head 168 and has a cylindrical inner wall 198 and a cylindrical outer wall 199 which are connected sealtightly at the ends and whose inner surfaces are covered with cohesive capillary structure 200.

Downwardly of the outlet opening 183 there is a nozzle ring 203 which cooperates with the outlet opening and which further cooperates with a nonillustrated conventional plunger.

FIG. 14 is a cross section through a heat pipe which can be used generally in the various embodiments according to the present invention, including the embodiment in FIGS. 12 and 13. The wall of the pipe is identified with reference numeral 205 and consists of a metal or ceramic, or other material which is inert and resistant with reference to the activity of the melt. In particular, the material of the wall 205 must not corrode and form oxides which would tend to color the melt. If this material itself is not corrosion resistant, then its outer sur face may be provided with a coating 206 of such corrosion-resistant material.

FIG. 15 is an enlarged view illustrating the cylindrical heat pipe 197 incorporated in the outlet opening 183 of the supply head 168.

In the embodiment of FIG. 16 the supply head 168 corresponding to that shown in FIGS. 12 and 13 utilizes-in place of or in addition to the other heat-exchange pipes-a helically convoluted heat pipe 210 which is arranged coaxially with the outlet opening 183. It is pointed out that because of the excellent thermal homogenization afforded by the heat pipe arrangements according to the various discussed embodiments, it is possible to entirely omit the turnable tube 185.

The embodiment illustrated in FIGS. 17 and 18 shows a supply conduit 213 with an associated supply head 214 of substantially rectangular cross section. Metallic plates 216 and 217 are provided of which the lower plate 216 is accommodated in a corresponding depression 219 in the bottom wall 220 of the construction. Each of the plates 216 and 217 is formed with an internal network 221 and 222, respectively, of heat pipes which are of course provided internally with capillary structure and vaporizable heat-exchange liquid. If the material of which the plates 216 and 217 are made is not corrosion resistant the necessary protection may be afforded by a coating 223, for instance of ceramic material, as shown in FIG. 19. Actually, the lower plate 216 will usually be adequate for effecting the desired control of the temperature of the melt. However, the upper plate 217 may be provided in addition where particular requirements exist, and will be supported (see FIG. 17) on supports 225 which may themselves consist of heat pipes or may be composed of material resistant to the vitreous melt.

In FIG. 20 I have illustrated a double drop nozzle ring 230 with two nozzles or outlets 231 and 232. A housing 235 consists of ceramic material in the illustrated embodiment, and into this housing there is inserted a bowl-shaped heat pipe structure 236 which covers the entire inner surface of the nozzle ring 230 circumferentially thereof. It will be seen that at the left-hand side of FIG. 20 the structure 236 is sealtightly inserted into the housing 235 and is adapted to be tempered at the outer side by a channel 238 which is also provided in the housing 235 and through which a heat-exchange medium flows in the direction indicated by the arrow and in contact with the outer side of the structure 236. At the right-hand side of FIG. 20 the structure 236 is supported on projections 240 which assure the presence of a hollow space 241 between the housing 235 and the outer surface of the structure 236. It will be appreciated that the possibility illustrated in the left-hand side of FIG. 20 and the possibility illustrated in the right-hand side of FIG. 20 can both be utilized in one and the same construction, or that they can each be utilized separately. If the possibility shown at the right-hand side of FIG. 20 is utilized separately, or in conjunction with that shown in the left-hand side, glass melt will enter into the space 241 in the direction of the arrows 242, and will fillbecause of an air escape opening 245 provided in the structure 236-the space surrounding the center section 247 of housing 235. This melt, which in effect constitutes a protective jacket, significantly reduces the danger of corrosion of the outer side of the structure 236 which would otherwise be present due to the contact with air which can enter by diffusion through the porous ceramic material of the housing 235 from the outer side of the ring 230 into contact with the outer side of the structure 236.

In FIG. 21 I have illustrated a single-drop nozzle ring 250 having a ceramic housing 251 which is exteriorly surrounded with a downwardly open cup-shaped heat pipe structure 252. In other respects this embodiment is analogous to the preceding one. If desired a temperature control device 254 may be associated with the outer side of the structure 252, and in the present embodiment this device 254 is configurated in ringshaped form with heat-exchange medium flowing in the direction of the arrow through its interior 255.

In FIG. 22 l have illustrated a melting crucible 310 which is of the type used when a vitreous melt of a particular characteristic, for instance for high-quality glass, it to be produced. The crucible 310 has an outer surface 313 and an inner surface 315 which is partially in contact with a body of vitreous melt 314. The surfaces 313 and 315 are provided on a sidewall 317 which, together with the bottom wall 318, outlines and surrounds the interior space of the crucible 310'. The left-hand side of FIG. 22 shows that both the sidewall 317 and the bottom wall 318 have inserted in them inserts 320 and 321 constructed as heat pipes and covered in their interior with capillary structure 323 and 324, respectively. The outer surface 313 at the left-hand side of FIG. 22 is surrounded by electrically heated conductors 325 concentric with the crucible 310 and provided with a continuous protective housing 327. Heating of the bottom wall 318 is effected by means of a gas burner 330 to which gas is supplied in the direction of the arrow 331 in controllable and regulatable manner through a valve 333.

The entire crucible 310 can be constructed in the manner illustrated in the left-hand side of FIG. 3. However, only onehalf can be so constructed and the other half can be constructed in the manner illustrated at the right-hand side, or the entire crucible can be constructed exclusively in the manner illustrated at the right-hand side. Here, the sidewall 317 and the bottom wall 318 are of double-walled construction, so that the inner and outer wall each define with one another a circumferntially extending continuous connected hollow space 335 which is covered on its interior surfaces with capillary structure 337. In this case heating is effected by means of electrical resistance heating conductors 339 embedded in the bottom wall 318.

A cover 340-is provided for the crucible 310 and a heat pipe 342 passes through the cover and extends to the immediate proximity of the bottom wall 318 where it is angled so as to extend in substantial parallelism with the bottom wall 318. The

purpose of the heat pipe 342 is to provide for a vertical homogenization of the temperature of the melt 314, that is to provide heat exchange between the inherently hotter and cooler vertically spaced strata of the melt, in order to make the temperature throughout the melt as uniform as possible. This may be necessary in certain circumstances, for instance if the size of the crucible 310 is such that the necessary and desired uniformity of temperature throughout the melt cannot be achieved only by the action of the heat pipe associated with the bottom and sidewalls. Exteriorly of the cover 340 a sleeve 345 surrounds the heat pipe 342 and heat exchange fluid can be passed throughthe sleeve in the direction of the arrows 346 and 347. Of course, other possibilities also exist.

FIG. 23 shows in addition to the insert 320 further axially I EXAMPLES are intended to be illustrative, rather than limitative, with reference to the construction and operation of various embodiments of the invention.

1. CRUCIBLE l Operating temperature range in C.:

Calcium Glasses with Glasses with natrium high alumihigh zircolead In the melt glass num content nium content glasses top 1,500 1,600 1,600-1 ,650 1,300 bottom L200 1.200-l ,300 1,300 1,100- l ,2

2. Structural details of heat pipes for use in circumstances shown under (l )2 a. Materials:

Pipe Heat Exchange Remarks Liquid TZM Li TZM titanium zirconium molybdenum. Mo is very advantageous and may he provided with protective coating where it extends outside the melt. Li This combination also does not color the melt. Ag Advantageous for special glass with high melting point.

b. The wall thickness of the heat pipe may be relatively small, because Li has only a low vapor pressure in the operating temperature ranges according to (l c. Generally, the material for the capillary structure should be the same as the material of the pipe.

(1. Construction of the capillary structure:

Wire nets. Second generation heat pipes, i.e., arterial heat pipes or in particular annular gap heat pipes, which render a relatively great rise of the heat-exchange liquid in other than-horizontal orientatiomThedepth of melt in conventional crucibles is between approximately and cm., and such rises are attainable with the heat pipes.

3. The heat pipes are able to transport greatheat quantities with very small temperature loss; having Li as heat-exchange medium at a temperature of for instance l,500 C., axial heat flow of up to 15 kw./cm. is attainable.

4. Start .up of the heat pipes presents no difficulties. lf necessary, the heat pipe is prewarmed to the vaporizing temperature of the heat-exchange medium.

ll. STORAGE OR SUPPLY VESSEL 1. Operating temperature range, e.g., for the glasses mentioned under ll 1 is between substantially 1,200-1 ,300 C. The temperature level is, basically speaking, lower than in the melting crucible. Peak temperatures are also lower. This increases the life expectancy of the heat pipes used.

2. Structural details of the heat pipes:

a. Materials:

Pipe Heat Exchange Medium Remarks TZM Li As in l/2/a W Li As in ll2/a Ta Li Ta does not color the melt.

b. Wall thickness of the pipe may be smaller than in l/2/b because the lower operating temperatures reduces both the corrosion danger and the vapor pressure of the heat exchange medium.

c. Same as in l/2/c.

d. Same as in l/2/d. The depth of melt in conventional supply vessels is about 60 cm. Therefore, lower rise heights than in I are required of the heat exchange medium.

Ill. SUPPLY CONDUIT AND HEAD 1. Operating temperature range is between 900 and 1,200 for all glasses which are produced in actual practice. 2. Structural details of the heat pipes:

b. As in ll/2/b.

c. As in l/2/c.

As in l/2/d. Depth of melt is only about 20 cm. Therefore, first generation heat pipes with lower rise capability of the heat exchange medium may be used.

3. Calculating the capacity of a 30 cm. long ring-gap heat pipe with Na as heat-exchange medium at a temperature of 1,100 C., a maximum axial heat transportation capability has been found of a. 6 kw./cm. if pipe is vertically oriented, and

b. 10 kw.lcm. if pipe is horizontally oriented.

4. Start up of the pipes is still less difficult here, because the heat-exchange media are at least in part low-temperature vaporizable.

lV. MELTING CRUCIBLE 1. Operating temperature range in the upper region of the melt is between substantially 1,300 and l ,600 C. 2. Structural details of heat pipes:

outside melt, for instance in wall of melting crucible.

b. As in l/2/d. Melt may have a depth of up to l m.

While it is thought that the above examples, related to the various embodiments, will aid in an understanding of the invention, it is again emphasized that they are not to be considered limiting in any sense.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 7

While the invention has been illustrated and described as embodied in an apparatus for treating glass melt, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the genericor specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A melting crucible for vitreous material, comprising wall means including a bottom wall surrounding and defining a melting chamber adapted to accommodate a body of vitreous melt to a predetermined level above said bottom wall; and heat-exchange means, including sealed conduit means extending from said level towards said bottom wall, capillary means accommodated in said conduit means, and a vaporizable heatexchange liquid in said conduit and circulating lengthwise of the same with alternate conversion from vaporized to liquid state solely due to the presence of a temperature differential at spaced points of said conduit resulting from differential temperature of said melt intermediate said level and said bottom wall.

2. A crucible as defined in claim 1, said conduit means being oriented in at least substantially vertical direction.

3. A crucible as defined in claim 1, said conduit means comprising at least two discrete conduits arranged lengthwise and each containing capillary means and vaporizable heatexchange liquid.

4. A crucible as defined in claim 3, wherein said conduits have adjacent end portions positioned to effect heat-exchange with one another.

5. A crucible as defined in claim 3, wherein said conduit means are exteriorly connected in heat-exchanging relationship.

6. A crucible as defined in claim 3, wherein said conduits have adjacent end portions positioned in overlapping relationship in direction lengthwise of said conduits.

7. A crucible as defined in claim 1, said conduit means comprising a conduit portion extending in at least substantial parallelism with said bottom wall at least proximal to the latter.

8. A crucible as defined in claim 1, said conduit means comprising a conduit portion extending in at least substantial parallelism with said level proximal to but below the same.

9. A melting crucible for vitreous material, comprising wall means, including a plurality of sidewalls and a bottom wall, together surrounding and defining a melting chamber adapted to accommodate a body of vitreous melt", a sealed interior space in at least one of said walls; capillary means in said space; and a body of vaporizable heat-exchange liquid in said space, circulating in the same and alternately vaporizing and condensing solely as a result of the presence of a temperature differential between two spaced points of said space in said one wall.

10. A crucible as defined in claim 9; further comprising at least one sealed heat-exchange conduit extending at least in part into said chamber and also accommodating'in its interior said capillary means and a quantity of said heat-exchange liquid.

11. A melting crucible for vitreous material, comprising wall means, including a plurality of sidewalls and a bottom wall, together surrounding and defining a melting chamber adapted to contain a body of vitreous melt; a plurality of recesses provided in at least one of said walls; and a plurality of hollow sealed inserts dimensioned to be receivable in the respective recesses, and each accommodating capillary means, and a body of vaporizable heat-exchange liquid which circulates in the interior of the respective insert and alternately vaporizes and condenses solely as a result of the pressure of a temperature differential between two spaced points of said insert.

12. A crucible as defined in claim 11; further comprising a conduit connecting at least two of said inserts with one another and also accommodating capillary structure and a quantity of said heat-exchange liquid.

13. A crucible as defined in claim 11; further comprising at least one sealed heat-exchange conduit extending at least in part into said chamber and also accommodating in its interior capillary means and a quantity of said heat-exchange liquid.

14. A crucible as defined in claim 13, said heat-exchange conduit having a portion located externally of said chamber; and further comprising control means for controlling the temperature of said portion and thereby the entire heat-exchange conduit.

15. A crucible as defined in claim 1; further comprising a storage vessel for melt and having an interior communicating with said chamber; and at least one three-dimensional structure composed of additional sealed conduit means analogous to the first-mentioned sealed conduit means, accommodated in said interior of said storage vessel.

16. A crucible as defined in claim 15, wherein said threedimensional structure extends throughout said interior.

17. A crucible as defined in claim 15, said structure comprising a plurality of straight additional heat'exchange conduits arranged so as to define with one another a three-dimensional grid.

18. A crucible as defined in claim 17, each of said additional heat-exchange conduits accommodating a body of said capillary structure, and wherein the capillary structures in at least some of said additional heat-exchange conduits are in contact with one another.

19. A crucible as defined in claim 15; further comprising control means for controlling the temperature of said threedimensional structure at the will of an operator.

20. A crucible as defined in claim 19, said structure extending at least in part out of said interior, and said control means being located exteriorly of said vessel and cooperating with said part.

21. A crucible as defined in claim 19, said control means being located interiorly of said vessel.

22. A crucible as defined in claim 19, wherein said control means comprises a cooling jacket at least in part surrounding said additional conduit means and defining therewith a clearance for circulation of a cooling fluid.

23. A crucible as defined in claim 22, wherein said cooling fluid is air.

24. A crucible as defined in claim 22, wherein said cooling fluid is water.

25. A crucible as defined in claim 20, wherein the melt is accommodated in said vessel to a predetermined level, said part penetrating said level; and further comprising anticorrosion means provided on said part at least where the latter penetrates said melt.

26. A crucible as defined in claim 25, wherein said anticorrosion means is a sleeve of platinum.

27. A crucible as defined in claim 15; further comprising a supply conduit having one end portion communicating with the interior of said storage vessel for receiving melt therefrom,

and an outer end portion spaced from said one end portion and to which melt flows from said one end portion; and further comprising at least one additional three-dimensional structure composed of said heat-exchange conduits accommodated in said supply conduit so as to be at least in part immersed in melt flowing from said one to said other end portion.

28. A crucible as defined in claim 27, said additional structure comprising a plurality of heat-exchange conduits extending proximal to a bottom wall of said supply conduit lengthwise of the same and at least one of said heat-exchange conduits having at least one end portion extending upwardly away from said bottom wall towards the upper level of melt in said supply conduit.

29. A crucible as defined in claim 28, said additional structure further comprising a plurality of substantially U-shaped heat-exchange conduits extending transversely of said supply conduit and having legs projecting upwardly away from said bottom wall.

30. A crucible as defined in claim 27, said additional structure comprising a plurality of substantially parallel straight heat-exchange conduits located in a plane paralleling the bottom wall of said supply conduit and each extending lengthwise of the latter.

31. A crucible as defined in claim 15; further comprising a supply conduit having one end communicating with said vessel for receiving melt therefrom, and an other end; a supply head having an interior space and being located at said other end in communication therewith for entry of said melt into said interior space; and at least one heat-exchange conduit system accommodated in said interior space for tempering of the melt in the same.

32. A crucible as defined in claim 31, said supply head having an outlet opening bounded by circumferential wall means; and wherein said circumferential wall means is constructed as a heat-exchange conduit accommodating capillary structure and vaporizable heat-exchange liquid.

33. A crucible as defined in claim 32, said wall means comprising an inner and an outer circumferential wall fluidtightly connected and defining with one another a sealed annular space accommodating said capillary structure and liquid.

34. A crucible as defined in claim 33, wherein said inner and outer walls are coaxial with one another and have respective interior surfaces facing said annular space and supporting said capillary structure.

35. A crucible as defined in claim 31, said supply head having an outlet communicating with said interior space; and wherein said heat-exchange conduit system comprises at least one at least part-circular heat exchange conduit arranged in said space coaxially with said outlet.

36. A crucible as defined in claim 35, said at least part-circular heat-exchange conduit comprising a projecting portion projecting into said other end of said supply conduit oppositely the direction of flow of melt from said supply conduit into said interior space.

37. A crucible as defined in claim 31, said supply head having an outlet communicating with said space; and said heatexchange conduit system comprising a helically convoluted heat-exchange conduit arranged in said space coaxially with said outlet.

38. A crucible as defined in claim 31, said heat-exchange conduit system comprising at least one plate-shaped element formed with a plurality of interior passages each of which constitutes a heat-exchange conduit.

39. A crucible as defined in claim 38, said interior space having a predetermined cross-sectional area and configuration, and wherein the area and outline of said plate-shaped element correspond at least substantially to said predetermined area and configuration.

40. A crucible as defined in claim 39, said plate-shaped element being arranged in at least substantial parallelism with the flow of said melt.

41. A crucible as defined in claim 38, said plate-shaped element being composed of a metallic material which is nonstaining with respect to said melt in response to contact with the same.

is composed of a ceramic material.

44. A crucible as defined in claim 38, said plate-shaped element extending in part from said interior space into said other I end of said supply conduit.

45. A crucible as defined in claim 31, said supply head having an outlet opening; further comprising a hollow nozzle ring downstream of said outlet opening for receiving melt from the same and defining a sealed inner annular passage; and capillary means and vaporizable heat-exchange liquid accommodated in saidpassage so that said nozzle ring constitutes a heat-exchange conduit.

46. A crucible as defined in claim 31, said supply head having an outlet opening; further comprising a nozzle ring downstream of said outlet opening for receiving melt therefrom and having at least one extrusion aperture; and heat-exchange conduit means surrounding said extrusion aperture exteriorly thereof.

47. A crucible as defined in claim 1, said heat-exchange conduit means comprising at least one heat-exchange conduit having a circumferential wall at least the outer surface of which is composed of material inert and resistant with respect to said vitreous melt.

48. A crucible as defined in claim 47, wherein said material is a ceramic material.

49. A crucible as defined in claim 47, wherein said material is a coating provided on said circumferential wall.

50. A crucible as defined in claim 47, said heat-exchange conduit having a portion which is located exteriorly of said melt; and a jacket of corrosion-resistant material surrounding at least said portion and defining therewith an annular clearance for accommodating a quantity of said melt.

51. A crucible as defined in claim 50, wherein said corrosion-resistant material is a ceramic material.

52. A crucible as defined in claim 50, said jacket having an outer side; and further comprising tempering means for tempering said outer side and thereby said heat-exchange conduit.

53. In a method of making vitreous articles, the steps of accommodating a vitreous melt in a container; conveying portions of said melt in a predetermined path from the container to a processing station; and affecting, upstream of said processing station, heat-exchange between said melt and at least one heat-exchange means wherein a vaporizable liquid travels in a closed circuit and alternately vaporizes and con denses solely in response to a temperature differential at spaced points of said circuit. 

1. A melting crucible for vitreous material, comprising wall means including a bottom wall surrounding and defining a melting chamber adapted to accommodate a body of vitreous melt to a predetermined level above said bottom wall; and heat-exchange means, including sealed conduit means extending from said level towards said bottom wall, capillary means accommodated in said conduit means, and a vaporizable heat-exchange liquid in said conduit and circulating lengthwise of the same with alternate conversion from vaporized to liquid state solely due to the presence of a temperature differential at spaced points of said conduit resulting from differential temperature of said melt intermediate said level and said bottom wall.
 2. A crucible as defined in claim 1, said conduit means being oriented in at least substantially vertical direction.
 3. A crucible as defined in claim 1, said conduit means comprising at least two discrete conduits arranged lengthwise and each containing capillary means and vaporizable heat-exchange liquid.
 4. A crucible as defined in claim 3, wherein said conduits have adjacent end portions positioned to effect heat-exchange with one another.
 5. A crucible as defined in claim 3, wherein said conduit means are exteriorly connected in heat-exchanging relationship.
 6. A crucible as defined in claim 3, wherein said conduits have adjacent end portions positioned in overlapping relationship in direction lengthwise of said conduits.
 7. A crucible as defined in claim 1, said conduit means comprising a conduit portion extending in at least substantial parallelism with said bottom wall at least proximal to the latter.
 8. A crucible as defined in claim 1, said conduit means comprising a conduit portion extending in at least substantial parallelism with said level proximal to but below the same.
 9. A melting crucible for vitreous material, comprising wall means, including a plurality of sidewalls and a bottom wall, together surrounding and defining a melting chamber adapted to accommodate a body of vitreous melt; a sealed interior space in at least one of said walls; capillary means in said space; and a body of vaporizable heat-exchange liquid in said space, circulating in the same and alternately vaporizing and condensing solely as a result of the presence of a temperature differential between two spaced points of said space in said one wall.
 10. A crucible as defined in claim 9; further comprising at least one sealed heat-exchange conduit extending at least in part into said chamber and also accommodating in its interior said capillary means and a quantity of said heat-exchange liquid.
 11. A melting crucible for vitreous material, comprising wall means, including a plurality of sidewalls and a bottom wall, together surrounding and defining a melting chamber adapted to contain a body of vitreous melt; a plurality of recesses provided in at least one of said walls; and a plurality of hollow sealed inserts dimensioned to be receivable in the respective recesses, and each accommodating capillary Means, and a body of vaporizable heat-exchange liquid which circulates in the interior of the respective insert and alternately vaporizes and condenses solely as a result of the pressure of a temperature differential between two spaced points of said insert.
 12. A crucible as defined in claim 11; further comprising a conduit connecting at least two of said inserts with one another and also accommodating capillary structure and a quantity of said heat-exchange liquid.
 13. A crucible as defined in claim 11; further comprising at least one sealed heat-exchange conduit extending at least in part into said chamber and also accommodating in its interior capillary means and a quantity of said heat-exchange liquid.
 14. A crucible as defined in claim 13, said heat-exchange conduit having a portion located externally of said chamber; and further comprising control means for controlling the temperature of said portion and thereby the entire heat-exchange conduit.
 15. A crucible as defined in claim 1; further comprising a storage vessel for melt and having an interior communicating with said chamber; and at least one three-dimensional structure composed of additional sealed conduit means analogous to the first-mentioned sealed conduit means, accommodated in said interior of said storage vessel.
 16. A crucible as defined in claim 15, wherein said three-dimensional structure extends throughout said interior.
 17. A crucible as defined in claim 15, said structure comprising a plurality of straight additional heat-exchange conduits arranged so as to define with one another a three-dimensional grid.
 18. A crucible as defined in claim 17, each of said additional heat-exchange conduits accommodating a body of said capillary structure; and wherein the capillary structures in at least some of said additional heat-exchange conduits are in contact with one another.
 19. A crucible as defined in claim 15; further comprising control means for controlling the temperature of said three-dimensional structure at the will of an operator.
 20. A crucible as defined in claim 19, said structure extending at least in part out of said interior, and said control means being located exteriorly of said vessel and cooperating with said part.
 21. A crucible as defined in claim 19, said control means being located interiorly of said vessel.
 22. A crucible as defined in claim 19, wherein said control means comprises a cooling jacket at least in part surrounding said additional conduit means and defining therewith a clearance for circulation of a cooling fluid.
 23. A crucible as defined in claim 22, wherein said cooling fluid is air.
 24. A crucible as defined in claim 22, wherein said cooling fluid is water.
 25. A crucible as defined in claim 20, wherein the melt is accommodated in said vessel to a predetermined level, said part penetrating said level; and further comprising anticorrosion means provided on said part at least where the latter penetrates said melt.
 26. A crucible as defined in claim 25, wherein said anticorrosion means is a sleeve of platinum.
 27. A crucible as defined in claim 15; further comprising a supply conduit having one end portion communicating with the interior of said storage vessel for receiving melt therefrom, and an outer end portion spaced from said one end portion and to which melt flows from said one end portion; and further comprising at least one additional three-dimensional structure composed of said heat-exchange conduits accommodated in said supply conduit so as to be at least in part immersed in melt flowing from said one to said other end portion.
 28. A crucible as defined in claim 27, said additional structure comprising a plurality of heat-exchange conduits extending proximal to a bottom wall of said supply conduit lengthwise of the same and at least one of said heat-exchange conduits having at least one end portion extending upwardly away from said bottom wall towards the upper level of Melt in said supply conduit.
 29. A crucible as defined in claim 28, said additional structure further comprising a plurality of substantially U-shaped heat-exchange conduits extending transversely of said supply conduit and having legs projecting upwardly away from said bottom wall.
 30. A crucible as defined in claim 27, said additional structure comprising a plurality of substantially parallel straight heat-exchange conduits located in a plane paralleling the bottom wall of said supply conduit and each extending lengthwise of the latter.
 31. A crucible as defined in claim 15; further comprising a supply conduit having one end communicating with said vessel for receiving melt therefrom, and an other end; a supply head having an interior space and being located at said other end in communication therewith for entry of said melt into said interior space; and at least one heat-exchange conduit system accommodated in said interior space for tempering of the melt in the same.
 32. A crucible as defined in claim 31, said supply head having an outlet opening bounded by circumferential wall means; and wherein said circumferential wall means is constructed as a heat-exchange conduit accommodating capillary structure and vaporizable heat-exchange liquid.
 33. A crucible as defined in claim 32, said wall means comprising an inner and an outer circumferential wall fluidtightly connected and defining with one another a sealed annular space accommodating said capillary structure and liquid.
 34. A crucible as defined in claim 33, wherein said inner and outer walls are coaxial with one another and have respective interior surfaces facing said annular space and supporting said capillary structure.
 35. A crucible as defined in claim 31, said supply head having an outlet communicating with said interior space; and wherein said heat-exchange conduit system comprises at least one at least part-circular heat exchange conduit arranged in said space coaxially with said outlet.
 36. A crucible as defined in claim 35, said at least part-circular heat-exchange conduit comprising a projecting portion projecting into said other end of said supply conduit oppositely the direction of flow of melt from said supply conduit into said interior space.
 37. A crucible as defined in claim 31, said supply head having an outlet communicating with said space; and said heat-exchange conduit system comprising a helically convoluted heat-exchange conduit arranged in said space coaxially with said outlet.
 38. A crucible as defined in claim 31, said heat-exchange conduit system comprising at least one plate-shaped element formed with a plurality of interior passages each of which constitutes a heat-exchange conduit.
 39. A crucible as defined in claim 38, said interior space having a predetermined cross-sectional area and configuration, and wherein the area and outline of said plate-shaped element correspond at least substantially to said predetermined area and configuration.
 40. A crucible as defined in claim 39, said plate-shaped element being arranged in at least substantial parallelism with the flow of said melt.
 41. A crucible as defined in claim 38, said plate-shaped element being composed of a metallic material which is nonstaining with respect to said melt in response to contact with the same.
 42. A crucible as defined in claim 38, said plate-shaped element being composed of a metallic material tending to stain said melt in response to contact therewith; and a coating of a material on said plate-shaped element which is nonstaining with respect to said melt.
 43. A crucible as defined in claim 42, wherein said coating is composed of a ceramic material.
 44. A crucible as defined in claim 38, said plate-shaped element extending in part from said interior space into said other end of said supply conduit.
 45. A crucible as defined in claim 31, said supply head having an outlet opening; further comprising a hollow nozzle ring downstream Of said outlet opening for receiving melt from the same and defining a sealed inner annular passage; and capillary means and vaporizable heat-exchange liquid accommodated in said passage so that said nozzle ring constitutes a heat-exchange conduit.
 46. A crucible as defined in claim 31, said supply head having an outlet opening; further comprising a nozzle ring downstream of said outlet opening for receiving melt therefrom and having at least one extrusion aperture; and heat-exchange conduit means surrounding said extrusion aperture exteriorly thereof.
 47. A crucible as defined in claim 1, said heat-exchange conduit means comprising at least one heat-exchange conduit having a circumferential wall at least the outer surface of which is composed of material inert and resistant with respect to said vitreous melt.
 48. A crucible as defined in claim 47, wherein said material is a ceramic material.
 49. A crucible as defined in claim 47, wherein said material is a coating provided on said circumferential wall.
 50. A crucible as defined in claim 47, said heat-exchange conduit having a portion which is located exteriorly of said melt; and a jacket of corrosion-resistant material surrounding at least said portion and defining therewith an annular clearance for accommodating a quantity of said melt.
 51. A crucible as defined in claim 50, wherein said corrosion-resistant material is a ceramic material.
 52. A crucible as defined in claim 50, said jacket having an outer side; and further comprising tempering means for tempering said outer side and thereby said heat-exchange conduit.
 53. In a method of making vitreous articles, the steps of accommodating a vitreous melt in a container; conveying portions of said melt in a predetermined path from the container to a processing station; and affecting, upstream of said processing station, heat-exchange between said melt and at least one heat-exchange means wherein a vaporizable liquid travels in a closed circuit and alternately vaporizes and condenses solely in response to a temperature differential at spaced points of said circuit. 